Fibreglass matting is a non - woven fabric made from extremely fine fibres of glass. These fibres are typically bonded together using a resin binder to form a flexible and durable mat - like material. The "100g" refers to the weight of the matting per square metre, which indicates its density and thickness characteristics. https://en.tm253.com/Product/Glass-Fiberglass-Chopped-Strand-Mat.html